This is a K23 Career Development Award application for Lisa M. McTeague, Ph.D., a clinical psychologist and Instructor in the Department of Psychiatry at Stanford University. Dr. McTeague's long-term career goal is to understand the neural basis of emotional reactivity impairments in severe affective illness in the service of identifying multimodal approaches to better remediate these deficits. This K23 award would enable Dr. McTeague to gain proficiency in 1) cutting-edge functional neuroimaging (fMRI), 2) transcranial magnetic stimulation (TMS) as a direct tool for investigating intact and disordered brain activation, 3) translating the principles of experimental medicine to psychosocial treatment toward ameliorating emotional dysfunction, and 4) leveraging these new techniques in conjunction with her established expertise in cognitive- behavioral treatment and psychophysiology for a series of grant submissions to help solidify her independence. This project focuses on posttraumatic stress disorder (PTSD) as a syndrome with well-characterized emotion deficits that may be susceptible to exogenous stimulation (i.e., TMS), which could, in turn, be utilized to enhance conventional psychotherapy outcomes. Trauma-focused exposure-based therapies are the first-line treatments for PTSD but half of patients meet diagnostic criteria upon completion. A fundamental component of exposure is the process of thorough emotional engagement-both subjectively and objectively-ensuring that the ultimate experience of habituation is optimally powerful. Dr. McTeague previously observed that chronic PTSD is marked by stark blunting of defensive mobilization, foremost in startle reflex responding during aversive imagery, suggestive of deficient limbic (and associated network) activation. To meaningfully advance these conclusions and point to intervention targets, Dr. McTeague proposes to assess brain activation and autonomic responding in 40 patients with PTSD and 20 trauma-exposed healthy participants during neutral and aversive as well as equally high arousing appetitive imagery. The inclusion of the latter will inform on whether PTSD is marked by core deficiencies in emotion networks as opposed to strategic avoidance-either outcome integral to intervention planning (Aim 1). To assess whether aberrant, state-dependent, interactions between limbic and prefrontal circuitry characterize PTSD, single pulses of TMS will be administered to two prefrontal regions during imagery (Aim 2). Finally, prefrontal-limbic circuits will be excited in patients with a single (non-therapeutic) session of rTMS to assess for (potentially normalizing) effects on emotional processing in an immediately subsequent imagery session (Aim 3). Successful completion would provide a more sophisticated neurobiological circuit understanding to Dr. McTeague's prior observation of blunted responding while furnishing essential guidance on the feasibility of using TMS to enhance emotional reactivity and regulation neurocircuitry as a preamble to imaginal exposure for PTSD (planned R01 application).